i boiled mine the same way but added dawn dish soap to cut the grease...coated the bottom of the pot to start with...then a good squirt every hour or so when i added a little water...when it was almost completely clean i changed the water and added more soap to try to get the grease out...the grease turns it yellow and makes it spotty..even after whittened...
to whitten mine, i wrapped the antlers in plastic wrap and electrical tape...taped and sealed good around the bases...then i bought a bunch of peroxide from the store...its cheap..like 2$ a big bottle...
i filled a bucket with the peroxide...enough to completely submerge the skull...then let it soak about 2 days...then took it out and rinsed it in clean water and let it sit in the sun for a day...
heres how mine turned out...
stay away from bleach!! it looks good for about a week...then turns chaulky and powdery..then yellows REAL quick...and the bone is soft and fragile and deteriorates by the day....the peroxide i used is holding up great..bone feels hard like it should and color is nice...if its not white enough, leave it in another day or 2...but let it dry an hour or 2 after a day and a half or 2 days...its whiter than it looks after it dries...id definently suggest whitening it somehow...